BACKGROUND OF THE INVENTION
Field of the Invention
[0001] Apparatuses and methods consistent with the present invention relate to a display
apparatus and a method for adjusting brightness thereof, and, more particularly, to
a display apparatus which is capable of adjusting brightness of a screen locally,
according to an incoming video signal, and a method for adjusting brightness thereof.
Description of the Related Art
[0002] Displays such as Liquid Crystal Displays (LCD) in TVs, laptops, or desktops represent
images thereon. Because these types of displays do not generate lights by themselves,
they require a separate light source to emit a ray of light. An LCD generally has
an LCD panel and a light emitting unit with a backlight at the back of the LCD panel,
and displays an image, while appropriately adjusting the LCD panel's transmissivity
for the light radiating from the light emitting unit.
[0003] Related art LCD generally use a uniform backlight for the light emitting unit, which
supplies light over the entire LCD panel in a uniform manner. When the uniform backlight
is used, all the images, including dark and bright images, are represented by the
light of the same level of brightness. Images including fireworks or explosions have
some parts that need be represented by higher brightness, but due to the absence of
counterbalance measures, it is difficult to represent lively images.
[0004] Additionally, the light generated at the uniform backlight falls onto the LCD panel,
causing interference. As a result, a LCD is unable to display zero-pixel image as
a true black image, and also has degradation of contrast ratio. Power consumption
also increases, because uniform backlight emits the same brightness light even for
a dark image which can be represented by a dimmer light.
SUMMARY OF THE INVENTION
[0005] Exemplary embodiments of the present invention address the above disadvantages and
other disadvantages not described above. Also, the present invention is not required
to overcome the disadvantages described above, and an exemplary embodiment of the
present invention may not overcome any of the problems described above.
[0006] According to the present invention there is provided an apparatus and method as set
forth in the appended claims. Other features of the invention will be apparent from
the dependent claims, and the description which follows.
[0007] The present invention provides a display apparatus capable of adjusting brightness
of light emitting unit in local areas of a screen, according to an incoming video
signal, and a method for adjusting brightness thereof.
[0008] The present invention also provides a display apparatus capable of pixel compensation
in local areas, to prevent loss of video signal due to a light emitting unit having
locally adjusted brightness, and a method for adjusting brightness thereof.
[0009] The present invention also provides a display apparatus capable of adjusting brightness
and compensating pixels with respect to an entire screen according to an incoming
video signal, and preventing unnecessary power consumption.
[0010] According to an aspect of the present invention, there is provided a display apparatus,
which may include a panel unit which displays a video signal, a light emitting unit
which provides the panel unit with a ray of light and causes the video signal to be
visualized, a light emission control unit which controls the light emitting unit so
that the ray of light is provided to each of local areas of the panel unit, and a
panel control unit which compensates pixels of the video signal in each of local areas,
to remove an artifact which is generated due to the ray of light provided to the local
areas of the panel unit.
[0011] The panel control unit compensates the pixels of the local areas, using representative
values which are computed by the light emission control unit to control the light
emitting unit.
[0012] The light emission control unit computes representative values according to the size
of RGB pixels of the respective local areas of the incoming video signal, so that
the light emitting unit is controlled to provide the panel unit with the ray of light
according to the representative values.
[0013] The panel control unit computes compensated R'G'B' pixels, by applying pixel compensation
coefficients to mathematical formula:

where R, G, B denote pixels before the compensation, R'G'B' denote pixels after the
compensation, and f
c denotes compensation coefficient.
[0014] The panel control unit computes the compensation coefficient using mathematical formula:

where f
c(i, j) denotes a compensation coefficient of the (i, j)th pixel, Thr denotes a parameter
for controlling a compensation gain, f
b(i, j) denotes an interpolated brightness of the (i, j)th pixel, LUT
BLU(f
b(i, j) denotes an interpolated f
b(i, j) based on the lookup table, Y(i, j)=max(R(i, j), G(i, j), B(i, j)), and LUT
GRAY(Y(i, j) denotes an interpolated value of Y(i, j) based on the lookup table.
[0015] The panel control unit computes the compensated brightness, by interpolating an estimate
brightness obtained by mathematical formula:

where f
E(m, n) denotes estimate brightness of the respective local areas of the (m×n) screen,
BLK_NUM denotes the total number of local areas, L
LD(k) denotes a representative value of a local area (k), and W
k(m, n) denotes optical profile data of (m, n)th local area (k).
[0016] The light emission control unit computes a local graylevel histogram of the greatest
pixel of the RGB pixels, and computes a local representative value using mathematical
formula:

where L
init(k) denotes an initial representative value of a local area (k), L_Thr denotes a predetermined
coefficient for the brightness compensation of the local area (k), BLK_NUM denotes
a total number of local areas, N
h denotes the number of graylevels, N
i denotes the number of pixels belonging to the (i)th graylevel of the graylevel histogram,
and M; denotes an average pixel of the (i)th graylevel of the graylevel histogram
of the local area (k).
[0017] The light emission control unit performs spatial and temporal filtering of the initial
representative value, and outputs a representative value for controlling the light
emitting unit.
[0018] The panel control unit compensates brightness of the entire screen in consideration
of the adjustment of the representative values by the pixels.
[0019] The light emission control unit computes a ratio by mathematical formula below, and
the representative values of the entire screen are adjusted uniformly according to
the computed ratio:

where R
GD denotes the ratio, A denotes a cut-off graylevel, and Thr2 denotes a threshold of
0-1.
[0020] The cut-off graylevel is the maximum graylevel which meets mathematical formula:

where g denotes 0 to 255 graylevels, H(g) denotes the number of pixels belonging to
graylevel (g), and Cut_Thr denotes a predetermined threshold at which there are a
plurality of pixels belonging to 0 to A graylevels.
[0021] The panel control unit computes R"G"B" pixels which are compensated by mathematical
formula:

where f
IIR denotes an Infinite Impulse Response (IIR) low pass filter, and γ denotes a gamma
compensation coefficient.
[0022] The panel control unit removes a contour artifact by dithering the R'G'B' pixels.
[0023] According to another aspect of the present invention, there is provided a method
for adjusting brightness of a display apparatus comprising a panel unit which displays
a video signal, and a light emitting unit which provides the panel unit with a ray
of light and causes the video signal to be visualized, which may include controlling
the light emitting unit so that the ray of light is provided to each of local areas
of the panel unit, and compensating pixels of the video signal in each of local areas,
to remove an artifact which is generated due to the ray of light provided to local
areas of the panel unit.
[0024] The compensating may include compensating the pixels of the local areas, using representative
values which are computed by the light emission control unit to control the light
emitting unit.
[0025] The controlling the light emitting unit may include computing representative values
according to the size of RGB pixels of the respective local areas of the incoming
video signal, so that the light emitting unit is controlled to provide the panel unit
with the ray of light according to the representative values.
[0026] The compensating the pixels may include computing compensated R'G'B' pixels, by applying
pixel compensation coefficients to mathematical formula:

where R, G, B denote pixels before the compensation, R'G'B' denote pixels after the
compensation, and f
c denotes compensation coefficient.
[0027] The compensating the pixels may include computing the compensation coefficient using
mathematical formula:

where f
c (i, j) denotes a compensation coefficient of the (i, j)th pixel, Thr denotes a parameter
for controlling a compensation gain, f
b(i, j) denotes an interpolated brightness of the (i, j)th pixel, LUT
BLU(f
b(i, j) denotes an interpolated f
b(i, j) based on the lookup table, Y(i, j)=max(R(i, j), G(i, j), B(i, j)), and LUT
GRAY(Y(i, j) denotes an interpolated value of Y(i, j) based on the lookup table.
[0028] The compensating the pixels may include computing the compensated brightness, by
interpolating an estimate brightness obtained by mathematical formula:

where f
E(m, n) denotes estimate brightness of the respective local areas of the (m×n) screen,
BLK_NUM denotes the total number of local areas, L
LD(k) denotes a representative value of a local area (k), and W
k(m, n) denotes optical profile data of (m, n)th local area (k).
[0029] The controlling the light emitting unit may include computing a local graylevel histogram
of the greatest pixel of the RGB pixels, and computes a local representative value
using mathematical formula:

where L
init(k) denotes an initial representative value of a local area (k), L_Thr denotes a predetermined
coefficient for the brightness compensation of the local area (k), BLK_NUM denotes
a total number of local areas, N
h denotes the number of graylevels, N
i denotes the number of pixels belonging to the (i)th graylevel of the graylevel histogram,
and M; denotes an average pixel of the (i)th graylevel of the graylevel histogram
of the local area (k).
[0030] The controlling the light emitting unit may include performing spatial and temporal
filtering of the initial representative value, and outputs a representative value
for controlling the light emitting unit.
[0031] Compensating brightness of the entire screen in consideration of the adjustment of
the representative values by the pixels, may be further provided.
[0032] Computing a ratio by mathematical formula below, and the representative values of
the entire screen may be adjusted uniformly according to the computed ratio:

where R
GD denotes the ratio, A denotes a cut-off graylevel, and Thr2 denotes a threshold of
0-1.
[0033] The cut-off graylevel is the maximum graylevel which meets mathematical formula:

where g denotes 0 to 255 graylevels, H(g) denotes the number of pixels belonging to
graylevel (g), and Cut_Thr denotes a predetermined threshold at which there are a
plurality of pixels belonging to 0 to A graylevels. Computing R"G"B" pixels, which
are compensated by mathematical formula, may be further provided:

where f
IIR denotes an Infinite Impulse Response (IIR) low pass filter, and γ denotes a gamma
compensation coefficient.
[0034] The compensating the pixels comprises removing a contour artifact by dithering the
R'G'B' pixels.
[0035] The light emitting unit comprises at least one of a plurality of light-emitting diodes,
a plurality of cold cathode fluorescent lamps, a plurality of field-effect diodes,
and a plurality of surface-conduction electron-emitter displays.
BRIEF DESCRIPTION OF THE DRAWING FIGURES
[0036] The above and other aspects of the present invention will be more apparent by describing
certain exemplary embodiments of the present invention with reference to the accompanying
drawings, in which:
FIG. 1 is a block diagram of a display apparatus according to an exemplary embodiment
of the present invention;
FIG. 2 is a block diagram of a light emission control unit of a display apparatus
according to an exemplary embodiment of the present invention;
FIG. 3 is a view provided for explaining a method for computing representative values
of a light emission control unit of a display apparatus according to an exemplary
embodiment of the present invention;
FIG. 4 is a view provided for explaining a method for adjusting brightness of entire
screen by a light emission control unit of a display apparatus according to an exemplary
embodiment of the present invention;
FIG. 5 is a block diagram of a panel control unit of a display apparatus according
to an exemplary embodiment of the present invention;
FIGS. 6 to 9 are views provided for explaining a method for compensating pixel values
of a panel control unit of a display apparatus according to an exemplary embodiment
of the present invention; and
FIG. 10 is a flowchart of a method for adjusting brightness of a display apparatus
according to an exemplary embodiment of the present invention.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE PRESENT INVENTION
[0037] Certain exemplary embodiments of the present invention will now be described in greater
detail with reference to the accompanying drawings.
[0038] In the following description, same drawing reference numerals are used for the same
elements even in different drawings. The matters defined in the description, such
as the detailed construction and elements, are provided to assist in a comprehensive
understanding of the invention. Thus, it is apparent that the present inventive concept
can be carried out without those specifically defined matters. Also, well-known functions
or constructions are not described in detail since they would obscure the invention
with unnecessary detail.
[0039] FIG. 1 is a block diagram of a display apparatus according to an exemplary embodiment
of the present invention.
[0040] Referring to FIG. 1, a display apparatus includes a video signal processing unit
100, a light emission control unit 200, a panel control unit 300, a light emitting
unit 400, and a panel unit 500.
[0041] The light emitting unit 400 includes a plurality of illuminating elements which generate
light, and is divided into a plurality of local areas. For example, the light emitting
unit 400 may be divided into 8×8 (that is, 64) local areas. Each of the local areas
include a one or more illuminating elements which are controlled to have the same
brightness, The illuminating elements may include a light-emitting diode (LED), cold
cathode fluorescent lamp (CCFL), field-effect diode (FED) or surface-conduction electron-emitter
display (SED).
[0042] The panel unit 500 adjusts transmissivity of light from the light emitting unit 400,
such that a video signal is visualized and displayed on a screen. The panel unit 500
includes two electrode-generated boards facing each other, and liquid crystal material
injected between these two boards. As the voltage is applied to the two electrodes,
electric field is generated, causing liquid crystal molecules between the two boards
to move and accordingly adjust light transmissivity.
[0043] The video signal processing unit 100 processes an incoming video signal to suit for
the resolution of the panel unit 500, and outputs as a RGB video signal.
[0044] The light emission control unit 200 controls the light emitting unit 400 according
to a RGB video signal output from the video signal processing unit 100, and accordingly
adjusts the brightness of the plurality of illuminating elements of the light emitting
unit 400. The light emission control unit 200 includes a local brightness adjusting
unit 210 and a general brightness adjusting unit 230.
[0045] The local brightness adjusting unit 210 controls the light emitting unit 400 to adjust
the local areas of the screen according to luminance value which is computed using
a RGB video signal. A representative value is computed using a RGB pixel of each of
the local areas, and used in the brightness adjustment of the illuminating elements
of the local areas.
[0046] The general brightness adjusting unit 230 adjusts the representative values of the
local areas according to the same ratio, so that the overall brightness of the screen
can be adjusted according to the brightness of the image being displayed on the screen.
That is, to represent a relatively dark image, the general brightness adjusting unit
230 controls the light emitting unit 400 so that the brightness of the entire screen
is decreased at the same ratio. The brightness of the entire screen may be adjusted
with reference to the R'G'B pixels being output from a local pixel compensating unit
310 which will be explained below.
[0047] The panel control unit 300 compensates the pixels to be displayed on the panel unit
500, using the RGB video signal being output from the video signal processing unit
100, so that the contrast ratio of the screen is enhanced. The panel control unit
300 includes a local pixel compensating unit 310, and a general pixel compensating
unit 330.
[0048] The local pixel compensating unit 310 compensates RGB pixels in respective local
areas, to offset the loss of video signal due to the local brightness adjustment of
the light emitting unit 400. The local pixel compensating unit 310 compensates the
RGB pixels to remove artefacts which are generated due to the brightness adjustment
of the local areas by the local brightness adjusting unit 210, and outputs the artifact-removed
pixels.
[0049] In particular, the local pixel compensating unit 310 estimates the brightness of
the respective local areas, after an optical profile for the screen is applied, using
the representative values which are computed at the local brightness adjusting unit
210. The local pixel compensating unit 310 then compensates the estimated brightness
to remove blocking artefacts. The local pixel compensating unit 310 then computes
compensation coefficients of the respective local areas using the compensated brightness,
and outputs R'G'B' pixels, which are the compensated RGB pixels, using the computed
compensation coefficients.
[0050] The general pixel compensating unit 330 is able to compensate for the variations
of brightness of the screen, as the general brightness adjusting unit 230 adjusts
the representative values of the local areas at the same ratio. That is, because the
general brightness adjusting unit 230 controls the light emitting unit 400 to cause
the overall brightness of the screen to be decreased at the same ratio, contrast ratio
is decreased in the dark area, and quality is deteriorated. In order to compensate
for this and to achieve representation of an image in its original brightness, the
R'G'B' pixels are obtained according to the adjustment ratio of the representative
values of the local areas, and output.
[0051] The construction and operation of the light emission control unit 200 and the panel
control unit 300 according to an exemplary embodiment of the present invention will
be explained below in greater detail.
[0052] FIG. 2 is a block diagram of a light emission control unit of a display apparatus
according to an exemplary embodiment of the present invention, and FIG. 3 is a view
provided for explaining a method for computing representative values of a light emission
control unit of a display apparatus according to an exemplary embodiment of the present
invention.
[0053] Referring to FIG. 2, the light emission control unit 200 includes the local brightness
adjusting unit 210 which includes a histogram computing unit 211, a brightness computing
unit 213, a spatial filtering unit 215 and a temporal filtering unit 217, and the
general brightness adjusting unit 230.
[0054] As illustrated in FIG. 3, the histogram computing unit 211 computes a graylevel histogram
with respect to a local area (k). The histogram computing unit 211 may compute a graylevel
histogram, using the pixels that meet the conditions expressed by the mathematical
formula 1:

where, Y(i,j) denotes brightness of a pixel at coordinates (i,j), R(I,j) denotes R-pixel
value of a pixel at coordinates (i,j), G(i,j) denotes G-pixel value of a pixel at
coordinates (i,j), and B(i,j) denotes B-pixel value of a pixel at coordinates (i,j).
Mathematical formula 1 represents that the largest value of the RGB pixels at coordinates
(i,j) is selected as the brightness for the pixel at coordinates (i,j). A graylevel
histogram is computed, based on the brightness of the pixels included in one local
area (k).
[0055] As in the example shown in FIG. 3, the histogram computing unit 211 computes a graylevel
histogram using mathematical formula 1, with respect to all the (1024×768) local areas
of the screen.
[0056] The brightness computing unit 213 computes initial representative value of the local
areas, by incorporating the graylevel histogram into mathematical formula 2:

where L
init(k) denotes an initial representative value of a local area (k), L_Thr denotes a predetermined
coefficient for the brightness compensation of the local area (k), BLK_NUM denotes
a total number of local areas, N
h denotes the number of graylevels, N
i denotes the number of pixels belonging to the (i)th graylevel of the graylevel histogram,
and M; denotes an average pixel of the (i)th graylevel of the graylevel histogram
of the local area (k). Referring to the example shown in FIG. 3, N
h=8, N
i is the number of pixels belonging to R0 to R7, and M; is the average pixel in R0
to R7.
[0057] The spatial filtering unit 215 spatially filters the initial representative value
L
init, and outputs the result. By applying initial representative values L
init to each of the local areas of the light emitting unit 400, blocking artefacts are
generated in a still image due to different brightness of the local areas. The initial
representative values L
init are spatially filtered through the spatial low pass filter to remove the blocking
artifacts, and as a result, a filtered, representative value L
s is output.
[0058] The temporal filtering unit 217 temporally filters the spatially-filtered representative
value L
s. When the spatially filtered representative value L
s is applied to the local areas of the light emitting unit 400, flickering occurs in
the motion image due to the different brightness of the local areas. The spatially
filtered representative value L
s is thus temporally filtered through a temporal low pass filter to remove the flickering.
As a result, a temporally filtered representative value L
LD is output.
[0059] The general brightness adjusting unit 230 adjusts the overall brightness of the screen,
using mathematical formula 3, according to the R'G'B' pixels which are compensated
and output from the local pixel compensating unit 310.

where L
out(k) denotes a final value for adjusting the brightness of the illuminating element(s)
of the local area (k), and R
GD denotes a ratio for adjusting the entire screen.
[0060] FIG. 4 is a view provided for explaining a method for adjusting brightness of entire
screen by a light emission control unit of a display apparatus according to an exemplary
embodiment of the present invention.
[0061] Referring to FIG. 4, the brightness of the entire screen is adjusted at the same
ratio R, and the ratio R is expressed by mathematical formula 4:

where R
GD denotes a ratio to adjust the overall brightness of the entire screen in a uniform
manner, A denotes a cut-off graylevel, which is the maximum graylevel of the pixels
of a local area excluding white Gaussian noise, and Thr2 denotes a threshold of 0-1.
[0062] The maximum graylevel (A) meets the mathematical formula 5:

where g denotes 0 to 255 graylevels, H(g) denotes the number of pixels belonging to
graylevel (g), and Cut_Thr denotes a predetermined threshold at which there are a
plurality of pixels belonging to 0 to A graylevels.
[0063] FIG. 5 is a block diagram of a panel control unit of a display apparatus according
to an exemplary embodiment of the present invention, and FIGS. 6 to 9 are views provided
for explaining a method for compensating pixel values of a panel control unit of a
display apparatus according to an exemplary embodiment of the present invention.
[0064] Referring to FIG. 5, the panel control unit 300 includes the local pixel compensating
unit 310 including a brightness estimating unit 311, a first LUT storage unit 314,
a brightness interpolating unit 313, a second LUT storage unit 314, a compensation
coefficient computing unit 315, a pixel compensating unit 316, and a dithering unit
317, and the general pixel compensating unit 330.
[0065] The brightness estimating unit 311 estimates brightness of each of the local areas,
by incorporating the representative value L
LD, obtained by the local brightness adjusting unit 210, into mathematical formula 6:

where f
E(m, n) denotes estimate brightness of the respective local areas of the (m×n) screen,
BLK_NUM denotes the total number of local areas, L
LD(k) denotes a representative value of a local area (k), and W
k(m, n) denotes optical profile data of (m, n)th local area (k).
[0066] The first LUT storage unit 314 stores the optical profile data as a lookup table
as illustrated in FIG. 5. FIG. 6 shows optical profile data which is measured from
the centre of each of the local areas, when a local area (k) is in on state, while
all the other local areas are in off state. As illustrated in FIG. 6, the local area
in on state has the greatest brightness, and the brightness gradually decreases towards
the local areas farther away from the local area in on state.
[0067] The brightness interpolating unit 313 interpolates (i, j)th pixel of each local area,
using the estimate brightness (f
E). As the representative value L
LD output from the local brightness adjusting unit 210 is applied by the light emitting
unit 400, the local areas each has the estimate brightness (f
E) as illustrated in FIG. 7, and as a result, blocking artefacts occur. Accordingly,
an interpolated pixel (f
b) of the (i, j)th pixel is computed to prevent the generating of the blocking artefacts,
by applying bi-cubic interpolation or bi-linear interpolation to the estimate brightness
(f
E).
[0068] The second LUT storage unit 314 stores lookup tables as the exemplary ones illustrated
in FIGS. 8A and 8B. In particular, the second LUT storage unit 314 stores a first
lookup table (LUT
BLU) for compensating the interpolated pixel (f
b) of the (i, j)th pixel, and a second lookup table LUT
GRAY for compensating a brightness Y of the (i, j)th pixel.
[0069] The compensation coefficient computing unit 315 computes a compensation coefficient,
using the lookup table of the second LUT storage unit 314 and mathematical formula:

where f
c (i, j) denotes a compensation coefficient of the (i, j)th pixel, Thr denotes a parameter
for controlling a compensation gain, f
b(i, j) denotes an interpolated brightness of the (i, j)th pixel, LUT
BLU(f
b(i, j) denotes an interpolated f
b(i, j) based on the lookup table, Y(i, j)=max(R(i, j), G(i, j), B(i, j)), and LUT
GRAY(Y(i, j) denotes an interpolated value of Y(i, j) based on the lookup table.
[0070] The pixel compensating unit 316 compensates the RGB pixel, using the compensation
coefficient computed at the compensation coefficient computing unit 315 and mathematical
formula below, and outputs a R'G'B' pixel:

where f
c denotes a compensation coefficient for a RGB pixel. According to mathematical formula
above, the smaller value is selected from among 255 and the pixel compensated by the
compensation coefficient, so that the R'G'B' pixel does not exceed the maximum brightness,
that is, 255, and cause saturation of an image.
[0071] The dithering unit 317 dithers the R'G'B' pixel being output from the pixel compensating
unit 316 and outputs the result. An image generally has a contour artifact when it
is represented using the R'G'B' pixel output from the pixel compensating unit 316,
but the contour artifact is removed by the dithering.
[0072] The general pixel compensating unit 330 compensates the overall brightness of the
screen, which is changed by the general brightness adjusting unit 230, using the dithered
R'G'B' pixel from the dithering unit 317. In particular, the general pixel compensating
unit 330 compensates the R'G'B' pixel using mathematical formula below, and outputs
the compensated R"G"B" pixel:

where Rre denotes a coefficient to compensate the overall brightness of the screen
which is changed by the general brightness adjusting unit 230. According to mathematical
formula 9, a smaller pixel is selected from among 255 and a pixel which is compensated
by the coefficient, such that the R"G"B" pixel does not exceed the maximum brightness,
that is, 255 and cause saturation of an image. Rre may be computed by incorporating
a ratio R
GD, which is the ratio used to adjust the overall brightness of the screen in a uniform
manner, to mathematical formula (see FIG. 9):

where f
IIR denotes an Infinite Impulse Response (IIR) low pass filter, and γ denotes a gamma
compensation coefficient.
[0073] FIG. 10 is a flowchart of a method for adjusting brightness of a display apparatus
according to an exemplary embodiment of the present invention.
[0074] Referring to FIG. 10, the local brightness adjusting unit 210 computes a representative
value L
LD of each local area (S600). The representative values L
LD are adjustment values which are used to control the light emitting unit 400 in each
of local areas to provide the panel unit 500 with a light, according to the size of
the RGB pixels for the respective local areas of the incoming signal.
[0075] The local pixel compensating unit 310 computes a R'G'B' pixel, after compensating
the loss of a video signal based on the representative value L
LD (S620). When controlling the light emitting unit 400 using the representative values
L
LD, different types of artifacts generally occur, hindering accurate representation
of an original image and sequentially deteriorating image quality. Accordingly, a
R'G'B' pixel is obtained from the incoming RGB pixel, by estimating the influence
of adjusting the light emitting unit 400 in each of local areas using the representative
values L
LD.
[0076] The general brightness adjusting unit 230 adjusts representative values L
LD according to the R'G'B' pixels, and computes the final values Lout (S640). In particular,
the general brightness adjusting unit 230 obtains the final values Lout, by adjusting
the representative values L
LD of the respective local areas based on the same ratio so that the overall brightness
of the entire screen is adjusted according to the R'G'B' pixels, and outputs the final
values Lout.
[0077] The general pixel adjusting unit 330 then computes R"G"B" pixels, by compensating
the brightness changes of the entire screen due to the final values Lout (S660). For
example, if the light emitting unit 400 is controlled by the general brightness adjusting
unit 230 to lower the overall brightness of the screen at the same ratio, the contrast
ratio in the relatively dark areas would generally deteriorate. Accordingly, the R'G'B'
pixels are compensated to R"G"B" pixels according to the ratio at which the representative
values of the respective local areas are adjusted, so that the image can be represented
with the brightness of the R'G'B' pixels.
[0078] Accordingly, it is possible to control the brightness of the screen and enhance contrast
ratio in each of local areas, so that the brightness of the entire screen can be adjusted.
The exemplary methods explained above are applicable not only to the LCDs, but to
other types of displays that represent video signals.
[0079] According to the exemplary embodiments of the present invention as explained above,
it is possible to adjust the brightness of the light emitting unit in each of local
areas, remove artifacts following the brightness adjustment, and improve contrast
ratio of the screen.
[0080] Furthermore, it is possible to adjust the brightness of the entire screen, compensate
for loss of image due to the adjustment, reduce power consumption, and improve image
quality efficiently.
[0081] The foregoing exemplary embodiments and advantages are merely exemplary and are not
to be construed as limiting the present invention. The present inventive concept can
be readily applied to other types of apparatuses. Also, the description of the exemplary
embodiments of the present invention is intended to be illustrative, and not to limit
the scope of the claims, and many alternatives, modifications, and variations will
be apparent to those skilled in the art.
[0082] Although a few preferred embodiments have been shown and described, it will be appreciated
by those skilled in the art that various changes and modifications might be made without
departing from the scope of the invention, as defined in the appended claims.
[0083] Attention is directed to all papers and documents which are filed concurrently with
or previous to this specification in connection with this application and which are
open to public inspection with this specification, and the contents of all such papers
and documents are incorporated herein by reference.
[0084] All of the features disclosed in this specification (including any accompanying claims,
abstract and drawings), and/or all of the steps of any method or process so disclosed,
may be combined in any combination, except combinations where at least some of such
features and/or steps are mutually exclusive.
[0085] Each feature disclosed in this specification (including any accompanying claims,
abstract and drawings) may be replaced by alternative features serving the same, equivalent
or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated
otherwise, each feature disclosed is one example only of a generic series of equivalent
or similar features.
[0086] The invention is not restricted to the details of the foregoing embodiment(s). The
invention extends to any novel one, or any novel combination, of the features disclosed
in this specification (including any accompanying claims, abstract and drawings),
or to any novel one, or any novel combination, of the steps of any method or process
so disclosed.
1. A display apparatus, comprising:
a panel (500) which displays a video signal;
a light emitter (400) which provides the panel (500) with a ray of light and causes
the video signal to be visualized;
a light emission controller (200) which controls the light emitting unit to provide
ray of light to each of local areas of the panel (500) in accordance with the brightness
values of the corresponding areas of the video signal; and
a panel controller (300) which compensates pixels of the video signal in each of the
local areas in accordance with the brightness values of the corresponding areas of
the video signal.
2. The display apparatus of claim 1, wherein the panel controller (300) compensates the
pixels of the local areas, using representative values of the brightness values which
are computed by the light emission controller to control the light emitter (400).
3. The display apparatus of claim 1, wherein the light emission controller computes representative
values according to the size of RGB pixels of the respective local areas of the incoming
video signal, so that the light emitter (400) is controlled to provide the panel (500)
with the ray of light according to the representative values.
4. The display apparatus of claim 2, wherein the panel controller (300) computes compensated
R'G'B' pixels, by applying pixel compensation coefficients to mathematical formula:

where R, G, B denote pixels before the compensation, R'G'B' denote pixels after the
compensation, and f
c denotes compensation coefficient.
5. The display apparatus of claim 4, wherein the panel controller (300) computes the
compensation coefficient using mathematical formula:

where f
c(i, j) denotes a compensation coefficient of the (i, j)th pixel, Thr denotes a parameter
for controlling a compensation gain, f
b(i, j) denotes an interpolated brightness of the (i, j)th pixel, LUT
BLU(f
b(i, j) denotes an interpolated f
b(i, j) based on the lookup table, Y(i, j)=max(R(i, j), G(i, j), B(i, j)), and LUT
GRAY(Y(i, j) denotes an interpolated value of Y(i, j) based on the lookup table.
6. The display apparatus of claim 5, wherein the panel controller (300) computes the
compensated brightness, by interpolating an estimate brightness obtained by mathematical
formula:

where f
E(m, n) denotes estimate brightness of the respective local areas of the (m x n) screen,
BLK_NUM denotes the total number of local areas, L
LD(k) denotes a representative value of a local area (k), and W
k(m, n) denotes optical profile data of (m, n)th local area (k).
7. The display apparatus of claim 3, wherein the light emission controller computes a
local graylevel histogram of the greatest pixel of the RGB pixels, and computes a
local representative value using mathematical formula:

where L
init(k) denotes an initial representative value of a local area (k), L_Thr denotes a predetermined
coefficient for the brightness compensation of the local area (k), BLK_NUM denotes
a total number of local areas, N
h denotes the number of graylevels, N
i denotes the number of pixels belonging to the (i)th graylevel of the graylevel histogram,
and M; denotes an average pixel of the (i)th graylevel of the graylevel histogram
of the local area (k).
8. The display apparatus of claim 7, wherein the light emission controller performs spatial
and temporal filtering of the initial representative value, and outputs a representative
value for controlling the light emitter (400).
9. The display apparatus of claim 2, wherein the panel controller (300) compensates brightness
of the entire screen in consideration of the adjustment of the representative values
by the pixels.
10. The display apparatus of claim 4, wherein the light emission controller computes a
ratio by mathematical formula below, and the representative values of the entire screen
are adjusted uniformly according to the computed ratio:

where R
GD denotes the ratio, A denotes a cut-off graylevel, and Thr2 denotes a threshold of
0-1.
11. The display apparatus of claim 10, wherein the cut-off graylevel is the maximum graylevel
which meets mathematical formula:

where g denotes 0 to 255 graylevels, H(g) denotes the number of pixels belonging to
graylevel (g), and Cut_Thr denotes a predetermined threshold at which there are a
plurality of pixels belonging to 0 to A graylevels.
12. The display apparatus of claim 10, wherein the panel controller (300) computes R"G"B"
pixels which are compensated by mathematical formula:

where f
IIR denotes an Infinite Impulse Response (IIR) low pass filter, and γ denotes a gamma
compensation coefficient.
13. The display apparatus of claim 1, wherein the light emitter (400) corresponding to
the local area comprises a plurality of light-emitting diodes, a plurality of cold
cathode fluorescent lamps, a plurality of field-effect diodes, or a plurality of surface-conduction
electron-emitter displays.
14. A method for adjusting brightness of a display apparatus comprising a panel unit which
displays a video signal, and a light emitting unit which provides the panel unit with
a ray of light and causes the video signal to be visualized, the method comprising:
controlling the light emitting unit so that the ray of light is provided to each of
local areas of the panel unit; and
compensating pixels of the video signal in each of local areas, to remove an artifact
which is generated due to the ray of light provided to local areas of the panel unit.
15. The method of claim 14, wherein the compensating comprises compensating the pixels
of the local areas, using representative values which are computed by the light emission
control unit to control the light emitting unit.
16. The method of claim 15, wherein the controlling the light emitting unit comprises
computing representative values according to the size of RGB pixels of the respective
local areas of the incoming video signal, so that the light emitting unit is controlled
to provide the panel unit with the ray of light according to the representative values.
17. The method of claim 15, wherein the compensating the pixels comprises computing compensated
R'G'B' pixels, by applying pixel compensation coefficients to mathematical formula:

where R, G, B denote pixels before the compensation, R'G'B' denote pixels after the
compensation, and f
c denotes compensation coefficient.
18. The method of claim 17, wherein the compensating the pixels comprises computing the
compensation coefficient using mathematical formula:

where f
c (i, j) denotes a compensation coefficient of the (i, j)th pixel, Thr denotes a parameter
for controlling a compensation gain, f
b(i, j) denotes an interpolated brightness of the (i, j)th pixel, LUT
BLU(f
b(i, j) denotes an interpolated f
b(i, j) based on the lookup table, Y(i, j)=max(R(i, j), G(i, j), B(i, j)), and LUT
GRAY(Y(i, j) denotes an interpolated value of Y(i, j) based on the lookup table.
19. The method of claim 18, wherein the compensating the pixels comprises computing the
compensated brightness, by interpolating an estimate brightness obtained by mathematical
formula:

where f
E(m, n) denotes estimate brightness of the respective local areas of the (m×n) screen,
BLK_NUM denotes the total number of local areas, L
LD(k) denotes a representative value of a local area (k), and W
k(m, n) denotes optical profile data of (m, n)th local area (k).
20. The method of claim 16, wherein the controlling the light emitting unit comprises
computing a local graylevel histogram of the greatest pixel of the RGB pixels, and
computes a local representative value using mathematical formula:

where L
init(k) denotes an initial representative value of a local area (k), L_Thr denotes a predetermined
coefficient for the brightness compensation of the local area (k), BLK_NUM denotes
a total number of local areas, N
h denotes the number of graylevels, N
i denotes the number of pixels belonging to the (i)th graylevel of the graylevel histogram,
and M; denotes an average pixel of the (i)th graylevel of the graylevel histogram
of the local area (k).
21. The method of claim 20, wherein the controlling the light emitting unit comprises
performing spatial and temporal filtering of the initial representative value, and
outputs a representative value for controlling the light emitting unit.
22. The method of claim 15, further comprising compensating brightness of the entire screen
in consideration of the adjustment of the representative values by the pixels.
23. The method of claim 17, further comprising computing a ratio by mathematical formula
below, and the representative values of the entire screen are adjusted uniformly according
to the computed ratio:

where R
GD denotes the ratio, A denotes a cut-off graylevel, and Thr2 denotes a threshold of
0-1.
24. The method of claim 23, wherein the cut-off graylevel is the maximum graylevel which
meets mathematical formula:

where g denotes 0 to 255 graylevels, H(g) denotes the number of pixels belonging to
graylevel (g), and Cut_Thr denotes a predetermined threshold at which there are a
plurality of pixels belonging to 0 to A graylevels.
25. The method of claim 23, further comprising computing R"G"B" pixels which are compensated
by mathematical formula:

where f
IIR denotes an Infinite Impulse Response (IIR) low pass filter, and γ denotes a gamma
compensation coefficient.